Topical issues in hydrogeology of seismogenic fault zones

The hydrogeology of fault zones, especially at considerable depth, is perhaps the most poorly developed area of earthquake source mechanics. This is due both to the insufficient data on the filtration characteristics of the geomaterial at large depths and to the complexity of the processes of mass transfer, fracture formation and healing under high temperatures and pressures. In these conditions, a fluid obviously has a very strong effect of on both the friction characteristics and the stress state in the vicinity of the slip zone. Fluids are carriers of dissolved matter and thermal energy, an effective catalyst for various types of metamorphic transformations. According to some models, fluid flows can be triggers for the start and stop of seismogenic ruptures. Constructing a complex computational model that adequately describes the processes of preparation, initiation, and stopping of various slip modes along faults, which is a recent trend in world seismology, requires developing the ideas about fluid dynamics of seismogenic faults. This review summarizes recent information on the hydrogeology of fault zones. Models and ideas about the role of fluids at different stages of the seismic cycle, derived from the field data, laboratory and in situ experiments, and numerical calculations, are analyzed.